ARUP; ISBN: 978-0-9562121-5-3 - CMBBE 2012 - Cardiff University

INTRODUCTION
The calcaneus is the most frequently fractured tarsal bone (65%) [1]. Fractures of the
calcaneus constitute 1% - 2% of all bone injuries [2]. There are two different types of
fractures. The extra- articular and intra- articular fracture type. The literature study
shows inconsistencies in treatment [1]. There are three different treatment strategies,
nonoperative (conservative), open reduction and internal fixation and primary
arthrodesis (both operative) [1–3]. Conservativly treated fractures showed more longterm
complications involving arthritis and malunion [4]. Operative treatment showed a
higher risk for wound dehiscence, wound infection and iatrogenic injury [4].
Patients with calcaneus fractures experience considerable interferences with daily living
activities. In general inadequate or inappropriate treatment leads to bony destruction and
deformity of the calcaneus and results in a functional loss.
The quality of anatomical reconstruction in calcaneus fracture fixation is important
because of its influence on the functional outcome. The functional outcome is nowadays
determined by various scores (American Orthopaedic Foot and Ankle Society (AOFAS)
hindfoot score, Maryland Foot Score (MFS), Creighton-Nebraska score (CN), gait
analysis (plantare pressure distribution, 3D gait analysis) or imaging procedures
(computer tomography (CT), plain radiographic) [5–7].
Only the imaging procedures have the opportunity to directly predict the quality of
anatomical reconstruction. The quality of reconstruction is usually reviewed by plain
radiographs or computer tomography (CT). The plain radiographic projections, makes it
possible to determine various angles (Böhler’s angle, Gissane’s angle) and distances
(length height, width) [7]. Several studies associated a restoration of Böhler’s angle with
a better outcome [8], [9]. Frequently there is no correlation between Böhler’s angle and
functional results of treatment. The plain radiography is not sufficient enough for the
evaluation of the anatomical reconstruction and to predict the functional outcome [7],
[10-13].
There are methods that measure the level of anatomical reconstruction in CT images
[10], [14]. However these methods again are based on a 2D way of looking at specific
CT slices. Currently no standardized 3D methods exist to analyse the quality of
individual anatomical reconstruction of the subchondral bone area of the joint surfaces.
The aim of this study was to develop an automatic algorithm based on CT images to
quantify the integrity of calcaneal subchondral bone area of the joint surfaces.
Validation of this algorithm was performed by assessing intra individual variations of
characteristic joint parameters in adults.
METHOD
The first step in joint surface analysis was to obtain accurate geometric models of the
anatomy from CT scan data. Bilateral upper limb CT data (slice thickness 0.625mm)
from 12 subjects (5 female, 7 male, 42 ±15 years) were manually segmented using
Amira ® (Visage Imaging, Richmond, Australia). 3D models from the calcaneus, talus
and cuboid were implemented in custom software programmed in MATLAB
(MathWorks, Inc; Natick, MA, USA). The software uses a nearest neighbour algorithm
to find the nearest point from the calcaneus to the talus or cuboid (Fig.1). All points
within a defined distance were assumed part of the joint surface. Three joint surfaces
(PSJ= posterior subtalar joint, CCJ= calcaneo- cuboid joint, AMSJ anterior medial
subtalar joint) were detected (Fig. 2).